Method of producing water-soluble nonturbid copolymers of at least one water-soluble N-vinyllactam and at least one hydrophobic comonomer

ABSTRACT

Method of producing vinyllactam copolymers by free-radical polymerization of at least one water-soluble N-vinyllactam and at least one hydrophobic comonomer in an organic solvent in the presence of an initiator under reflux conditions, where N-vinyllactam is added to the reflux.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing water-solublecopolymers of at least one water-soluble N-vinyllactam and at least onehydrophobic comonomer by free-radical polymerization of the monomers inan organic solvent, and to the copolymers obtainable by the method andtheir use.

The production of copolymers from N-vinyllactams and hydrophobiccomonomers by free-radical polymerization is known. The production ofsuch copolymers takes place in an organic solvent, for example analcohol or in a mixture of water and organic solvent with a high contentof solvent. Usually, the polymerization is carried out under reflux ofthe solvent. The hydrophobic monomers that are more readily volatilecompared to the N-vinyllactams pass in this way into the gas phase andinto the condensate.

For many application purposes, copolymers are desired which dissolve inwater to give clear solutions, i.e. the FNU value of a 5% strength byweight solution should be <20. However, there is the problem thatdiffering reactivities and differing polarity of the monomers can leadto increases in the concentration of the hydrophobic monomers whichresults in homopolymers which are not water-soluble being able to beformed from the hydrophobic monomers. Even in small amounts in the rangefrom 500 to 1000 ppm, such homopolymers lead to turbidity of an aqueoussolution of the copolymers. The increases in concentration ofhydrophobic monomers can arise in particular in the gas phase and in thecondensate, and also on the reactor wall and the surface of thepolymerization medium.

U.S. Pat. No. 5,395,904 describes the polymerization of vinylpyrrolidoneand vinylacetate by controlled polymerization according to the feedmethod. An alcoholic solvent is used which can comprise up to 50% byweight of water.

U.S. Pat. No. 5,319,041 describes the preparation of copolymers ofvinylpyrrolidone and vinyl acetate by polymerization according to thefeed method with control of the polymerization temperature.

U.S. Pat. No. 5,502,136 describes a method of producing copolymers ofvinylpyrrolidone and vinyl acetate according to the feed method, wherethe feeds are controlled via a scheme defined by specific mathematicalformulae.

U.S. Pat. No. 4,520,179 and U.S. Pat. No. 4,554,311 describe thepolymerization of vinylpyrrolidone and vinyl acetate with t-butylperoxypivalate as initiator in water or water/alcohol mixtures. Theinitiator used therein allows the production of copolymers with a narrowmolecular weight distribution, that does not lead to water-solubleproducts with a FNU value of <20.

EP-A 161 describes a method of producing copolymers of vinylpyrrolidoneand vinyl acetate where, after the polymerization, an afterpolymerization with specific initiators is carried out. However, thepolymers have high residual contents of vinyl acetate and are notsufficiently nonturbid.

EP-A 795 567 describes the production of copolymers of vinyllactams andhydrophobic monomers by polymerization in aqueous solution.

EP-A discloses the production of copolymers of vinylpyrrolidone andvinyl esters which dissolve in water to give clear solutions, where, ata certain point during the polymerization, a solvent exchange is carriedout in order to remove volatile constituents. This method is relativelycomplex.

DE-A 22 18 935 describes the copolymerization of N-vinylpyrrolidone withvarious water-soluble and water-insoluble comonomers. Use is made hereof water-insoluble initiators which are used in the form of a finelydivided suspension in an aqueous solution of the copolymers. However, inthe case of the water-insoluble comonomers, this does not likewise leadto the desired water-soluble copolymers with a FNU value of <20.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide an improvedmethod of producing clearly water-soluble copolymers of at least onehydrophilic N-vinyllactam and at least one hydrophobic comonomer byfree-radical copolymerization in an organic solvent.

According to the invention, the object is achieved by free-radicalpolymerization of at least one water-soluble N-vinyllactam and at leastone hydrophobic comonomer in an organic solvent in the presence of aninitiator under reflux conditions, wherein N-vinyllactam is added to thereflux.

DETAILED DESCRIPTION OF THE INVENTION

Suitable water-soluble vinyllactams are N-vinylpyrrolidone,3-methyl-N-vinylpyrrolidone, 4-methyl-N-vinylpyrrolidone,5-methyl-N-vinylpyrrolidone, N-vinylpyridone, N-vinylpiperidone,N-vinylcaprolactam, preferably N-vinylpyrrolidone. The vinyllactams areused in amounts of from 30 to 90% by weight, preferably 50 to 90% byweight.

The method according to the invention is suitable for producingwater-soluble polymers of monomer mixtures whose content of hydrophobicmonomers is in the range from 10 to 70% by weight, preferably 10 to 50%by weight, based on the monomer mixture. Suitable hydrophobic monomersare those with a solubility in water in the range from 1 to 100 g/l.Suitable hydrophobic monomers are, for example, vinyl acetate, vinylpropionate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butylacrylate, t-butyl acrylate, methyl methacrylate, ethyl methacrylate,acrylonitrile or methacrylonitrile. The hydrophobic monomers are inparticular those whose boiling points at atmospheric pressure are in therange of the polymerization temperature from 60 to 130° C., so that theycan evaporate under polymerization conditions. Even at a boiling pointslightly below the polymerization temperature, the hydrophobic monomercan pass into the gas phase with the solvent if there is adequatemiscibility with the solvent and the solvent boils. A preferredhydrophobic monomer is vinyl acetate.

Free-radical initiators which may be mentioned are, for example, dialkylor diaryl peroxides, such as di-tert-amyl peroxide, dicumyl peroxide,bis(tert-butylperoxyisopropyl)benzene,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, tert-butyl cumeneperoxide, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexene,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)butane ordi-tert-butyl peroxide, aliphatic and aromatic peroxy esters, such ascumyl peroxyneodecanoate, 2,4,4-trimethylpentyl 2-peroxyneodecanoate,tert-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-amylperoxypivalate, tert-butyl peroxypivalate, tert-amylperoxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butylperoxydiethylacetate, 1,4-bis(tert-butylperoxy)cyclohexane, tert-butylperoxyisobutanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate,tert-butyl peroxyacetate, tert-amyl peroxybenzoate or tert-butylperoxybenzoate, dialkanoyl or dibenzoyl peroxides, such as diisobutanoylperoxide, bis(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide,didecanoyl peroxide, 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexaneor dibenzoyl peroxide, and peroxycarbonates, such asbis(4-tert-butylcyclohexyl) peroxydicarbonate, bis(2-ethylhexyl)peroxydicarbonate, di-tert-butyl peroxydicarbonate, diacetylperoxydicarbonate, dimyristyl peroxydicarbonate, tert-butylperoxyisopropylcarbonate or tert-butyl peroxy-2-ethylhexylcarbonate.Readily oil-soluble azo initiators used are, for example,2,2′-azobis(isobutyronitrile), 2,2′-azobis(2,4-dimethylvaleronitrile) or4,4′-azobis(4-cyanopentanoic acid).

The free-radical initiator used is preferably a compound chosen from thegroup comprising tert-butyl peroxy-2-ethylhexanoate (Trigonox® 21;Trigonox® grades from Akzo Nobel), tert-amyl peroxy-2-ethylhexanoate(Trigonox® 121), tert-butyl peroxybenzoate (Trigonox® C), tert-amylperoxybenzoate, tert-butyl peroxyacetate (Trigonox® F), tert-butylperoxy-3,5,5-trimethylhexanoate (Trigonox® 42 S), tert-butylperoxyisobutanoate, tert-butyl peroxydiethylacetate (Trigonox® 27),tert-butyl peroxypivalate (Trigonox® 25), tert-butylperoxyisopropylcarbonate, (Trigonox® BPIC),2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (Trigonox® 101),di-tert-butyl peroxide (Trigonox® B), cumyl hydroperoxide (Trigonox® K)and tert-butyl peroxy-2-ethylhexylcarbonate (Trigonox® 117). It is ofcourse also possible to use mixtures of the abovementioned oil-solublefree-radical initiators.

The amount of initiator used, based on the monomers, is in the rangefrom 0.02 to 15 mol %, preferably 0.05 to 3 mol %. In the methodaccording to the invention, the initiator is used as solution, dependingon the solubility, in an organic solvent. Preferably, the same solventas also serves as polymerization medium is chosen. The initiators areparticularly preferably used in a C1-C4-alcohol. In these solutions theinitiator concentration is in the range from 0.02 to 2 mol %, preferably0.1 to 2 mol %, based on the solvent.

A suitable polymerization medium is a polar organic solvent. The solventmust be so hydrophilic that it is miscible with the vinyllactam in anymixing ratio which is achieved during the polymerization reaction. Inaddition, the solvent should boil under the polymerization conditions sothat a reflux can form. Of suitability are, for example, aliphatic oraromatic halogenated hydrocarbons, such as chloroform, carbontetrachloride, hexachloroethane, dichloroethane, tetrachloroethane,chlorobenzene, and liquid C1- or C2-chlorofluorohydrocarbons, aliphaticC2- to C5-nitriles, such as acetonitrile, propionitrile, butyronitrileor valeronitrile, linear or cyclic aliphatic C3- to C7-ketones, such asacetone, methyl ethyl ketone, methyl isobutyl ketone, 2- or 3-hexanone,2-, 3-, or 4-heptanone, cyclopentanone, cyclohexanone, linear or cyclicaliphatic ethers, such as diisopropyl ether, 1,3- or 1,4-dioxane,tetrahydrofliran or ethylene glycol dimethyl ether, carbonates, such asdiethyl carbonate, and lactones, such as butyrolactone, valerolactone orcaprolactone. Suitable mono-, di- or polyhydric alcohols are, inparticular, the C1- to C8-alcohols, the C2- to C8-alkanediols, and C3-to C10-tri- or polyols. Examples thereof are methanol, ethanol,n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol,n-pentanol, 2-pentanol, 3-pentanol, and ethylene glycol, propyleneglycol or 1,3-propanediol.

The monoalkoxy alcohols used are, in particular, the abovementioned C1-to C8-alcohols and C2- to C8-alkanediols, and C3- to C10-triolssubstituted by a C1- to C6-alkoxy group. Examples thereof aremethoxymethanol, 2-methoxyethanol, 2-methoxypropanol, 3-methoxypropanol,2-methoxybutanol, 3-methoxybutanol, 4-methoxybutanol, 2-ethoxyethanol,2-ethoxypropanol, 3-ethoxypropanol, 2-ethoxybutanol, 3-ethoxybutanol,4-ethoxybutanol, 2-isopropoxyethanol, 2-isopropoxypropanol,3-isopropoxypropanol, 2-isopropoxybutanol, 3-isopropoxybutanol,4-isopropoxybutanol, 2-(n-propoxy)ethanol, 2-(n-propoxy)propanol,3-(n-propoxy)propanol, 2-(n-propoxy)butanol, 3-(n-propoxy)butanol,4-(n-propoxy)butanol, 2-(n-butoxy)ethanol, 2-(n-butoxy)propanol,3-(n-butoxy)propanol, 2-(n-butoxy)butanol, 3-(n-butoxy)butanol,4-(n-butoxy)butanol, 2-(sec-butoxy)ethanol, 2-(sec-butoxy)propanol,3-(sec-butoxy)propanol, 2-(sec-butoxy)butanol, 3-(sec-butoxy)butanol,4-(sec-butoxy)butanol, 2-(tert-butoxy)ethanol, 2-(tert-butoxy)propanol,3-(tert-butoxy)propanol, 2-(tert-butoxy)butanol, 3-(tert-butoxy)butanol,4-(tert-butoxy)butanol.

Of particular suitability is a C1- to C4-alcohol, preferably ethanol orisopropanol. Particular preference is given to using isopropanol assolvent.

The polymerization is usually carried out at a neutral pH in the rangefrom 5 to 9. If necessary, the pH is adjusted and/or maintained byadding a base, such as ammonia, triethylamine, triethanolamine, NaOH, oran acid, such as hydrochloric acid, formic acid, acetic acid, lacticacid, oxalic acid.

If relatively low molecular weights are desired, these can beestablished by adding a regulator to the polymerization mixture.Suitable regulators are, for example, aldehydes, such as formaldehyde,acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde,formic acid, ammonium formate, hydroxylammonium sulfate andhydroxylammonium phosphate. In addition, regulators can be used whichcomprise sulfur in organically bonded form. These are, for example,di-n-butyl sulfide, di-n-octyl sulfide, diphenyl sulfide, diisopropyldisulfide, di-n-butyl disulfide, di-n-hexyl disulfide, diacetyldisulfide and di-t-butyl trisulfide. Preferably, the regulators comprisesulfur in the form of SH groups. Examples of such regulators are n-butylmercaptan, n-hexyl mercaptan or n-dodecyl mercaptan. Particularpreference is given to water-soluble, sulfur-containing polymerizationregulators, such as, for example, hydrogen sulfites, disulfites andcompounds such as ethyl thioglycolate, cysteine, 2-mercaptoethanol,1,3-mercaptopropanol, 3-mercaptopropane-1,2-diol, 1,4-mercaptobutanol,mercaptoacetic acid, 3-mercaptopropionic acid, mercaptosuccinic acid,thioglycerol, diethanol sulfide, thiodiglycol, ethylthioethanol,thiourea and dimethyl sulfoxide. Further suitable regulators are allylcompounds, such as allyl alcohol or allyl bromide, benzyl compounds,such as benzyl chloride or alkyl halides, such as chloroform ortetrachloromethane. In a preferred embodiment, the regulator is meteredinto the reaction mixture, if appropriate, as a solution in aC1-C4-alcohol.

In the method according to the invention, the monomers, if appropriateas solution in a C1-C4-alcohol, are metered into the reaction mixture(feed method). In one embodiment of the invention, up to 30% by weight,preferably up to 25% by weight, of the water-soluble N-vinyllactam I(based on the total amount of N-vinyllactam I) and a small amount of theinitiator solution and solvent, preferably ethanol or isopropanol, areinitially introduced. Then, the mixture is brought to the reactiontemperature and the remaining amount of monomer is metered incontinuously or in several portions at the same time as the remainder ofinitiator solution and, if appropriate, a regulator. In general, themetered addition takes place over a period of from 2 to 14 hours,preferably 3 to 12 hours, ideally 4 to 10 hours. Preferably, vinyllactamand hydrophobic comonomer are metered in so that the feeds are completeat the same time. The concentration of the monomers in the reactionmixture is in the range from 10 to 80% by weight, preferably 15 to 70%by weight, based on the reaction mixture. In this case, after thereaction mixture has been brought to the desired reaction temperature,the initiator solution is metered in continuously or in severalportions, in particular over a period of from 2.5 to 16 hours, ideally 5to 12 hours.

The polymerization reaction is carried out under reflux conditions. Inthis connection, reflux conditions means that the liquid polymerizationmixture boils and the readily volatile components, such as the solventand/or the hydrophobic monomers, evaporate and condense again as aresult of cooling. Reflux conditions are maintained by controllingtemperature and pressure.

The reaction temperature can be 60 to 150° C., it is usually in therange from 60 to 90° C. The reaction can be carried out at atmosphericpressure, under autogenous pressure or under protective-gas gagepressure. In the case of protective-gas gage pressure, the pressure isregulated so that boiling is still always present. The person skilled inthe art can determine suitable pressure ranges using the relative vaporpressures. Usually, the pressure here will not exceed 2 MPa.

The polymerization takes place in a boiler equipped with a stirringdevice. Suitable stirring devices are anchor stirrers, propellerstirrers, cross-blade stirrers, Mik stirrers, and other types ofstirrers suitable for solution polymerizations which are known to theperson skilled in the art. In addition, one or more feed devices formetering the monomers, the initiator solution, and, if appropriate, theregulator (solutions) are also present.

In addition, the boiler, in the upper region of the reactor where noliquid polymerization mixture but a gas phase, is present, is equippedwith a condenser.

Under the polymerization conditions, on account of their lower boilingpoints, solvents and hydrophobic monomers pass in part into the gasphase, whereas the higher-boiling N-vinyllactam remains in the liquidpolymerization phase. In the condenser, the gaseous mixture of solventand hydrophobic monomers condenses and thus forms the so-called reflux.

According to the method of the invention, vinyllactam is added to thereflux. The amount of vinyllactam is chosen here so that the amount ofvinyllactam which is consumed per time unit through polymerization ispartly or completely added to the reflux of hydrophobic monomer and inso doing is passed to the reaction mixture in the boiler. The amount ofhydrophobic monomer consumed in each case per time unit is, by contrast,added directly to the reaction mixture. The amount of vinyllactamconsumed per time unit can be calculated using the copolymerizationparameters, or be determined by taking a sample during an experiment.The parameters relevant for this purpose are the copolymerizationparameters of the monomers used, and also the equations required for thecalculation, which are accessible to the person skilled in the art fromknown text books and publications. For the example of vinylpyrrolidoneand vinyl acetate as comonomers, the relevant calculations have beendetailed, for example, in U.S. Pat. No. 5,395,904. A separatecalculation depending on the choice of monomers is easy to carry out bythe person skilled in the art.

Accordingly, the method is carried out in a manner which involves addingsome of the vinyllactam directly to the reaction mixture, if appropriatemetering some directly into the reaction mixture, and adding some viathe reflux of the hydrophobic monomer from the condenser. Some of thehydrophobic monomer is added directly to the reaction mixture, and someis metered in subsequently during the course of the reaction dependingon consumption with some of the hydrophobic monomer always being in thegas phase and in the reflux until the end (complete conversion) of thepolymerization.

Within the scope of the invention, it is likewise possible that thevinyllactam is only metered into the reflux of hydrophobic monomer ormonomer and solvent toward the end of the reaction if the majority ofmonomers has taken place through normal metering directly to thereaction mixture, and the majority of vinyllactam has been consumed bypolymerization. On account of the copolymerization parameters, at thispoint in time, the amount of vinyllactam is lower than that ofhydrophobic monomer, meaning that polymer fractions would arise whichcomprise large proportions of hydrophobic monomer, or that homopolymersof hydrophobic monomer would form. This can be effectively prevented bythe vinyllactam, which is usually metered directly into the reactionmixture subsequently, being metered in via the reflux in order, in sodoing, to provide significantly more effective mixing with the refluxthat is rich in hydrophobic monomer without this metered addition, andthus prevent high local concentrations of hydrophobic monomer in thereaction mixture at the position of the reflux into the reaction mixtureand thus the described disadvantages.

The metering time of the vinyllactam to the reflux takes place at thestart of the polymerization, with either some of the vinyllactam beingadded to the reaction mixture before or at the start of the reaction(addition of the initiator), and the remainder of vinyllactam to bemetered being mixed into the reflux via a continuously controlledaddition (linear or nonlinear course of the amounts of vinyllactam pertime unit), before it flows back into the reaction mixture or is meteredinto this. In another embodiment of the invention, the reaction takesplace as already revealed in the prior art via a controlled addition(linear or nonlinear course of the amounts of vinyllactam and/orhydrophobic monomer per time unit) of the monomers by reference to themetering scheme calculated on the basis of the copolymerizationparameters. Finally, toward the end of the polymerization time (70 to100% of the addition time of the hydrophobic monomer), the dosing of afurther amount of vinyllactam takes place through metered addition tothe reflux of the hydrophobic monomer. This further dosing of thevinyllactam, however, lasts longer by at least 10 to 40% of the totaladdition time of the hydrophobic monomer after the end of the additionof the hydrophobic monomer and is, if appropriate, also continued to theend if the reflux of the hydrophobic monomer becomes weaker and isbarely still detectable.

In order to ascertain the suitable amounts, the reflux profile for thedesired composition is firstly ascertained in each case. For this, theconcentration of the vinyl ester in the reflux per time unit isdetermined for the entire course of the polymerization reaction.

fter the polymerization reaction, if desired, one or more polymerizationinitiators are additionally added and the polymer solution is heated,e.g. to the polymerization temperature or to temperatures above thepolymerization temperature, in order to complete the polymerization. Ofsuitability are the azo initiators stated above, but also all othercustomary initiators suitable for a free-radical polymerization inalcoholic solution, for example peroxides, hydroperoxides,peroxodisulfates, percarbonates, peroxoesters and hydrogen peroxide.Through this, the polymerization reaction is conducted to a conversionof 99.9%. The solutions which form during the polymerization usuallycomprise 10 to 70% by weight, preferably 15 to 60% by weight, ofpolymer. After the polymerization, the solutions obtained can also besubjected to a physical after treatment, for example steam distillationor stripping with nitrogen, with the solvent or impurities volatile withsteam being removed from the solution. In addition, a chemicalafter-treatment or bleaching, for example with hydrogen peroxide orsodium sulfite/tert-butyl hydroperoxide, can also take place.

The aqueous solutions of the copolymer obtained by steam distillationcan, if appropriate, be converted into solid powders by a drying processcorresponding to the prior art. Suitable drying processes are thosewhich are suitable for drying from aqueous solution. Preferred processesare, for example, spray-drying, spray fluidized-bed drying, drum-dryingand belt-drying. Freeze-drying and freeze-concentration can likewise beused.

The polymers obtained generally have a K value (determined at 25° C. ina 1% strength by weight aqueous or ethanolic solution) in the range from10 to 100, in particular 15 to 90 and particularly preferably 20 to 80.Determination of the K value is described in H. Fikentscher “Systematikder Cellulosen auf Grund ihrer Viskosität in Lösung” [systematics of thecelluloses based on their viscosity in solution], Cellulose-Chemie 13(1932), 58-64 and 71-74, and Encyclopedia of Chemical Technology, Vol.21, 2nd edition, 427-428 (1970).

A measure of their clear solubility is the nephelometric turbidity unitFNU (or NTU), which is measured at 25° C. in a 5% strength by weightaqueous solution of the polymer and is fixed by calibration withformazin as artificial opacifier. The precise method is given in thecourse of the examples below. The polymers obtained according to theinvention have a FNU value of <20, in particular <10, preferably <7 andparticularly <5.

The polymers obtained by the method according to the invention are usedin particular in cosmetic and pharmaceutical preparations, for exampleas thickeners or film formers in hair lacquer additives, hair settingadditives or hairspray additives, in skin cosmetic preparations,immunochemicals or as active ingredient-releasing agent inpharmaceutical preparations. In addition, the polymers producedaccording to the invention can be used as auxiliaries for agrochemistry,for example for seed coating or for slow-release fertilizerformulations. In addition, the polymers can also be used as coatings forindustrial applications, such as coating of paper or plastics. Thepolymers are also suitable for use in hot-melt adhesives. Furthermore,these polymers are suitable as binders for transfer printing, aslubricant additives, as rust inhibitors or rust removers from metallicsurfaces, as scale inhibitors or scale removers, as auxiliaries duringthe recovery of petroleum from oil-containing water, as auxiliariesduring the production of petroleum and natural gas, and thetransportation of petroleum and natural gas, as cleaners ofwaste-waters, as adhesive raw materials, as detergent additives, and asauxiliaries in the photo industry.

The examples listed below are intended to illustrate the inventionwithout, however, limiting it.

EXAMPLES

The turbidity of the aqueous copolymer solution was determined bynephelometric turbidity measurement (modified method according to DIN38404). In this method, the light scattered by the measurement solutionis determined photometrically, light scattering being caused by theinteraction between the light beams and the particles or droplets in thesolution, the number and size of which constitute the degree ofturbidity. The quantity being measured here is the nephelometricturbidity unit FNU (or NTU), which is measured at 25° C. in a 5%strength by weight aqueous solution of the polymer and is fixed bycalibration with formazin as artificial opacifier. The higher the FNUvalue, the more turbid the solution.

General procedure: Feed material allocation Amount Unit Initial chargeof feed 1 as stated of feed 2 3.2 g isopropanol 30 g Feed 1 isopropanol270 g vinylpyrrolidone as stated vinyl acetate as stated Feed 2isopropanol 50 g tert-butyl perpivalate 75% 2 g Feed 3 vinylpyrrolidoneas stated Feed 4 isopropanol 50 g tert-butyl perpivalate 75% 2 gtert-butyl perpivalate: 75% in mineral oil (Trigonox ® 25)

The polymerization was carried out in a stirred reactor with a volume of2 l. The reactor was equipped with an ascending condenser which wasprovided in the lower section with an inlet valve for feed 3. Theinitial charge was flushed with nitrogen for 10 min and heated to thepolymerization temperature (internal temperature). At the polymerizationtemperature minus 10%, feeds 1 and 2 were started.

Meter in feed 1 in a hours, feed 2 in b hours, return feed 3 in c hoursmixed with the reflux to the reactor.

After-polymerize for 1 h. The system was then heated to an internaltemperature of polymerization temperature plus 10% and feed 4 wasmetered in over d hours at this temperature. When feed 4 was complete,the mixture was after-polymerized for a further 2 h at this temperature.The majority of the solvent was then removed by distillation, andresidual amounts were removed by means of steam distillation. During thesteam distillation, water was added as required to maintainstirrability. After cooling, water was used, if appropriate, toestablish the particular solids content.

Solids content in % by weight

K value measured 1% strength in ethanol

GC analysis: vinylpyrrolidone in ppm; vinyl acetate in ppm;

Appearance: color, clarity, FNU value

All experiments: residual monomers: vinyl acetate <10 ppm

The data in mol % referred to the total amount of the component inquestion.

Comparative Example

VP/VAc = 55.5:44.5 mol mol % Initial charge: VP 0.142 8.470 VAc 0.1739.953 Feed 1 VP 1.536 91.530 VAc 1.563 90.047 Feed 3 VP 0.000 0.000

a=4 hours, b=6 hours, c=--, d=1.5 hours

Temperature: 70° C.

Appearance: yellowish, turbid, FNU: 106

Residual monomers: vinylpyrrolidone 36 ppm

Example 1

VP/VAc = 55.5:44.5 mol mol % Initial charge: VP 0.142 8.470 VAc 0.1739.953 Feed 1 VP 1.000 59.590 VAc 1.563 90.047 Feed 3 VP 0.536 31.940

a=4 hours, b=6 hours, c=6,5, d=1.5 hours

Temperature: 70° C.

Appearance: slightly yellowish, clear, FNU: 7

Residual monomers: vinylpyrrolidone <10 ppm

Example 2

at VP/VAc = 70:30 mol mol % Initial charge: VP 0.179 7.838 VAc 0.1169.050 Feed 1 VP 1.401 61.281 VAc 1.171 90.950 Feed 3 VP 0.706 30.881

a=4 hours, b=6 hours, c=6,5, d=1.5 hours

Temperature: 70° C.

Appearance: slightly yellowish, clear, FNU: 3

Residual monomers: vinylpyrrolidone <10 ppm

Example 3

at VP/VAc = 30:70 mol mol % Initial charge: VP 0.077 7.806 VAc 0.2729.050 Feed 1 VP 0.605 61.496 VAc 2.732 90.950 Feed 3 VP 0.302 30.697

a=6 hours, b=9 hours, c=10, d=2.5 hours

Temperature: 70° C.

Appearance: slightly yellowish, clear, FNU: 11

Residual monomers: vinylpyrrolidone 15 ppm

Example 4

at VP/VAc = 60:40 mol mol % Initial charge: VP 0.154 7.806 VAc 0.1559.050 Feed 1 VP 1.209 61.446 VAc 1.561 90.950 Feed 3 VP 0.605 30.748

a=4 hours, b=6 hours, c=6.5, d=1.5 hours

Temperature: 70° C.

Appearance: slightly yellowish, clear, FNU: 1.5

Residual monomers: vinylpyrrolidone <10 ppm

Example 5

at VP/VAc = 50:50 mol mol % Initial charge: VP 0.128 7.809 VAc 0.1949.050 Feed 1 VP 1.007 61.440 VAc 1.951 90.950 Feed 3 VP 0.504 30.751

a=4.5 hours, b=7 hours, c=8, d=2 hours

Temperature: 70° C.

Appearance: slightly yellowish, clear, FNU: 3

Residual monomers: vinylpyrrolidone <10 ppm

1. A method of producing vinyllactam copolymers, the method comprising:(a) providing at least one water-soluble N-vinyllactam and at least onehydrophobic comonomer; and (b) free-radical polymerizing the at leastone water-soluble N-vinyllactam and the at least one hydrophobiccomonomer in an organic solvent in the presence of an initiator underreflux conditions such that a reflux comprising a condensing gaseousmixture is present, wherein at least a portion of the at least onewater-soluble N-vinyllactam is added to the reflux.
 2. The methodaccording to claim 1, wherein the hydrophobic comonomer comprises amonomer having a solubility in water of 1 to 100 g/l.
 3. The methodaccording to claim 1, wherein the hydro phobic comonomer comprises amonomer having a boiling point at atmospheric pressure of 60 to 150° C.4. The method according to claim 2, wherein the hydro phobic comonomercomprises a monomer having a boiling point at atmospheric pressure of 60to 150° C.
 5. The method according to claim 1, wherein the hydrophobiccomonomer comprises a monomer selected from the group consisting ofvinyl acetate, vinyl propionate, methyl acrylate, ethyl acrylate,n-propyl acrylate, n-butyl acrylate, t-butyl acrylate, methylmethacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, andmixtures thereof.
 6. The method according to claim 4, wherein thehydrophobic comonomer comprises a monomer selected from the groupconsisting of vinyl acetate, vinyl propionate, methyl acrylate, ethylacrylate, n-propyl acrylate, n-butyl acrylate, t-butyl acrylate, methylmethacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, andmixtures thereof.
 7. The method according to claim 1, wherein thehydrophobic comonomer comprises vinyl acetate.
 8. The method accordingto claim 4, wherein the hydrophobic comonomer comprises vinyl acetate.9. The method according to claim 1, wherein the N-vinyllactam comprisesN-vinylpyrrolidone.
 10. The method according to claim 8, wherein theN-vinyllactam comprises N-vinylpyrrolidone.
 11. The method according toclaim 1, wherein the polymerization is carried out at a temperature of60 to 150° C.
 12. The method according to claim 10, wherein thepolymerization is carried out at a temperature of 60 to 150° C.
 13. Themethod according to claim 1, wherein the organic solvent comprises analcohol.
 14. The method according to claim 12, wherein the organicsolvent comprises an alcohol.